Considerable time and effort has been devoted to characterizing pathways of hormonal carcinogenesis with few clear results, although progress can be reported on the general theme of proto-oncogene activation/control/function. This proposal addresses a new approach to identify both molecular events and genes (proto-oncogenes/anti-oncogenes) involved in hormonal carcinogenesis of Syrian hamsters where 100% frequency of leiomyosarcoma induction is observed. Studies will be carried out based upon the hypothesis that hormones induce tumors by upregulating viral long terminal repeats (LTR), which induce retrotransposition, resulting in insertional mutation and neoplasia. There are three interrelated specific aims to accomplish our objectives. SPECIFIC AIM 1 is to characterize enhancer-promoter activity of the hamster retroviral LTR subcloned into pSVOCAT. This will establish that the LTR is transcriptionally active, therefore, suitable for use in Specific Aim 2. SPECIFIC AIM 2 has three parts. First, we will establish and validate that the APH(3')II neomycin- resistant gene, interrupted by insertion of an intron, is inactive in bacteria but active in eukaryotic cells. Second, we will construct and test retrotransposons. Third, we will establish and clone cells stably transfected with the above retrotransposons. SPECIFIC AIM 3 will be to mutagenize stably transfected cells (hormones, growth factors, oncogenes, tumor promoters). The resultant transformed of the integration sites by recovery of the spliced APH(3')II gene and associated genomic DNA. Finally, genes contiguous with integration sites will be characterized for their contribution to the neoplastic process. In the future, based on successful completion of Specific Aim 3, transgenic mice an hamsters containing retrotransposons will be established. Ultimately, tracking of retrotransposition frequency and tissue specificity in the transgenic animals has potential for helping define pathways of hormonal and chemical carcinogenesis, as well as in elucidating the role of retroviral DNA in this process. Extension of this model to human hormonally related neoplastic disease such as prostate, breast, or uterine cancer is feasible in view of the increasing numbers of retroviral elements identified in the human genome.